Crystallization apparatus, crystallization method, and phase shifter

ABSTRACT

A crystallization apparatus includes an illumination system which applies illumination light for crystallization to a non-single-crystal semiconductor film, and a phase shifter which includes first and second regions disposed to form a straight boundary and transmitting the illumination light from the illumination system by a first phase retardation therebetween, and phase-modulates the illumination light to provide a light intensity distribution having an inverse peak pattern that light intensity falls in a zone of the non-single-crystal semiconductor film containing an axis corresponding to the boundary. The phase shifter further includes a small region which extends into at least one of the first and second regions from the boundary and transmits the illumination light by a second phase retardation with respect to the at least one of the first and second regions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2002-262249, filed Sep. 9,2002, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a crystallization apparatus,crystallization method, and phase shifter applied to anon-single-crystal semiconductor film such as a polycrystalline oramorphous semiconductor film, particularly to a crystallizationapparatus, crystallization method, and phase shifter for modulating aphase of laser light to be applied to the non-single-crystalsemiconductor film in the crystallization.

2. Description of the Related Art

Materials of thin film transistors (TFT) for use as switching devicesfor controlling voltages to be applied to pixels, for example, of aliquid crystal display (LCD) have heretofore been roughly divided intoamorphous silicon and poly-silicon.

The mobility of the poly-silicon is higher than that of the amorphoussilicon. Therefore, when the poly-silicon is used to form thin filmtransistors, a switching speed increases and the display responds morequickly as compared with the use of the amorphous silicon. Such thinfilm transistors are also usable as components of peripheral LSIcircuits. Furthermore, there is an advantage that design margins ofother components can be reduced. When peripheral circuits such as adriver circuit and DAC are integrated on the display, these peripheralcircuits are operable at a higher speed.

Although the poly-silicon includes a number of crystal grains, themobility thereof is lower than that of single-crystal silicon. When thepoly-silicon is used to form a small-sized transistor, this raises aproblem that the number of crystal grain boundaries fluctuates within achannel region. In recent years, crystallization methods for producingsingle-crystal silicon grains of a large diameter have been proposed inorder to improve the mobility and reduce the fluctuation in the numberof crystal grain boundaries within the channel region.

For this type of crystallization method, “phase-modulated Excimer LaserAnnealing (ELA)” has heretofore been known that applies excimer laserlight to a non-single-crystal semiconductor film via a phase shifter(phase-shift mask) disposed in parallel with and in the proximity of thesemiconductor film to produce a crystallized semiconductor film. Detailsof the phase-modulated ELA are disclosed, for example, in “AppliedSurface Science Vol. 21, No. 5, pp. 278 to 287, 2000”.

In the phase-modulated ELA, the light intensity distribution of thelight applied to the non-single-crystal semiconductor film is controlledin a zone corresponding to a phase-shift section of the phase shifter tohave an inverse peak pattern (that is, a pattern in which the lightintensity significantly increases according to an increase in thedistance from the center of the zone). As a result, a temperaturegradient is generated in the semiconductor film of a molten stateaccording to the light intensity distribution, and a crystal nucleus iscreated at a part of the semiconductor film which first coagulatesaccording to the light intensity of substantially 0. Then, a crystalgrows in a lateral direction toward the outside from the crystal nucleus(lateral growth), thereby forming a single-crystal grain of a largediameter.

Conventionally, the phase shifter for general use is a so-called linearphase shifter, which includes pairs of rectangular regions having aphase retardation π (180 degrees) therebetween and repeatedly arrangedin one direction. In this case, a straight boundary between two regionsserves as the phase-shift section, and therefore the light intensity onthe non-single-crystal semiconductor film is controlled to have aninverse peak pattern in which the light intensity is substantially 0 ata location of an axis corresponding to the phase-shift section andone-dimensionally increases according to an increase in the distancefrom the location.

In the conventional art in which the aforementioned linear phase shifteris used, a temperature distribution is lowest on an axis correspondingto the phase-shift section, and a temperature gradient is generated in adirection perpendicular to the axis corresponding to the phase-shiftsection. That is, the crystal nucleus is created on the axiscorresponding to the phase-shift section, and crystallization proceedsfrom the crystal nucleus in the direction perpendicular to the axiscorresponding to the phase-shift section. As a result, the crystalnucleus is created on the axis corresponding to the phase-shift section,but a position on the axis where the crystal nucleus is created isindefinite. In other words, in the conventional art, it has beenimpossible to specify the creation point of the crystal nucleus, and ithas also been impossible to two-dimensionally control a region where thecrystal grain is formed.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a crystallizationapparatus, crystallization method, and phase shifter, which cantwo-dimensionally control a region where a single-crystal grain isformed.

According to a first aspect of the present invention, there is provideda crystallization apparatus comprising: an illumination system whichapplies illumination light for crystallization to a non-single-crystalsemiconductor film; a phase shifter which includes first and secondregions disposed to form a straight boundary and transmitting theillumination light from the illumination system by a first phaseretardation therebetween, and phase-modulates the illumination light toprovide a light intensity distribution having an inverse peak patternthat light intensity falls in a zone of the non-single-crystalsemiconductor film containing an axis corresponding to the boundary; thephase shifter further including a small region which extends into atleast one of the first and second regions from the boundary andtransmits the illumination light from the illumination system by asecond phase retardation with respect to the at least one of the firstand second regions.

According to a second aspect of the present invention, there is provideda crystallization method comprising: applying illumination light forcrystallization to a non-single-crystal semiconductor film;phase-modulating the illumination light by using a phase shifter whichincludes first and second regions disposed to form a straight boundaryand transmitting the illumination light by a first phase retardationtherebetween, to provide a light intensity distribution having aninverse peak pattern that light intensity falls in a zone of thenon-single-crystal semiconductor film containing an axis correspondingto the boundary; and transmitting the illumination light through a smallregion, which is formed in the phase shifter to extend into at least oneof the first and second region from the boundary, by a second phaseretardation with respect to the at least one of the first and secondregions.

According to a third aspect of the present invention, there is provideda phase shifter comprising: first and second regions disposed to form astraight boundary and transmitting illumination light by a first phaseretardation therebetween, and a small region which extends into at leastone of the first and second regions from the boundary and transmits theillumination light by a second phase retardation with respect to the atleast one of the first and second regions.

In these crystallization apparatus, crystallization method, and phaseshifter, a crystal nucleus is created at a position limited by the smallregion of the phase sifter, and crystallization proceeds from thecrystal nucleus in a growth direction limited one-dimensionally. Thus,the position of a crystal grain boundary is substantially controllable.That is, it is possible to two-dimensionally control a region where asingle-crystal grain is formed, by specifying the positions of thecrystal nucleus and the crystal grain boundary.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is a diagram schematically showing the configuration of acrystallization apparatus according to a first embodiment of the presentinvention;

FIGS. 2A and 2B are plan and perspective views schematically showing theconfiguration of a basic segment in a phase shifter shown in FIG. 1;

FIGS. 3A to 3D are diagrams for explaining the function of a linearphase shifter;

FIGS. 4A to 4D are diagrams for explaining the function of a circularphase shifter;

FIGS. 5A to 5C are diagrams for briefly explaining the function of thephase shifter shown in FIGS. 2A and 2B;

FIG. 6 is a diagram for explaining the function of the phase shiftershown in FIGS. 2A and 2B in further detail;

FIGS. 7A and 7B are graphs showing a light intensity distributionobtained along a line A—A crossing a circular part corresponding to thephase-shift section in numeric value examples in which the numericalaperture NA1 for an illumination light is set to NA1=0 and NA1=0.1;

FIG. 8 is a diagram schematically showing the configuration of thecrystallization apparatus according to a second embodiment of thepresent invention;

FIG. 9 is a plan view for schematically showing the configuration of abasic segment in the phase shifter shown in FIG. 8;

FIGS. 10A and 10B are diagrams showing the alignment between a crystalgrain and a channel formed in each embodiment in comparison with that ofa related art;

FIGS. 11A and 11B are diagrams showing a growth angle estimated from thestart point of crystal growth of the crystal grain formed in eachembodiment in comparison with that of the related art;

FIGS. 12A to 12E are sectional views showing steps of producing anelectronic device using the crystallization apparatus of eachembodiment;

FIG. 13 is a plan view showing a position of a transistor produced asthe electronic device in FIGS. 12A to 12E;

FIG. 14 is a diagram schematically showing the circuit configuration ofa liquid crystal display containing the transistor shown in FIG. 13; and

FIG. 15 is a diagram schematically showing a sectional structure of theliquid crystal display shown in FIG. 14.

DETAILED DESCRIPTION OF THE INVENTION

A crystallization apparatus according to a first embodiment of thepresent invention will be described hereinafter with reference to theaccompanying drawings.

FIG. 1 is a diagram schematically showing the configuration of thecrystallization apparatus. The crystallization apparatus includes anillumination system 2 which illuminates a phase shifter 1. Theillumination system 2 includes a KrF excimer laser source 2 a whichsupplies a laser light having a wavelength, for example, of 248 nm. Itis to be noted that the light source 2 a may be replaced by anotherappropriate light source such as an XeCl excimer laser source. The laserlight from the light source 2 a is enlarged via a beam expander 2 b andsubsequently incident upon a first fly eye lens 2 c.

The first fly eye lens 2 c has a focal surface provided on the rear sidethereof and serves as a plurality of light sources. Luminous fluxes fromthese light sources illuminate an incidence surface of a second fly eyelens 2 e via a first condenser optical system 2 d in an overlappedmanner. The second fly eye lens 2 e has a focal surface provided on therear side thereof and serves as light sources more than those in thefocal surface of the first fly eye lens 2 c. Luminous fluxes from thelight sources in the focal surface of the second fly eye lens 2 eilluminate the phase shifter 1 via a second condenser optical system 2 fin an overlapped manner.

The first fly eye lens 2 c and first condenser optical system 2 dconstitute a first homogenizer, and an incidence angle on the phaseshifter 1 is homogenized by the first homogenizer. The second fly eyelens 2 e and second condenser optical system 2 f constitute a secondhomogenizer, and an in-plane position on the phase shifter 1 ishomogenized by the second homogenizer. Thus, a light having asubstantially homogenous light intensity distribution is applied fromthe illumination system 2 to the phase shifter 1.

The phase shifter 1 is disposed in parallel with and the proximity witha sample substrate 3 for crystallization, and phase-modulates the laserlight to be applied from the illumination system 2 to the samplesubstrate 3. The sample substrate 3 is obtained, for example, by formingamorphous silicon film on an underlying film covering a glass plate fora liquid crystal display by a chemical vapor growth method. The phaseshifter 1 is disposed to face the amorphous semiconductor film. Thesample substrate 3 is placed at a predetermined position on a substratestage 4 and held by a vacuum or electrostatic chuck.

FIGS. 2A and 2B are plan and perspective views schematically showing theconfiguration of a basic segment in the phase shifter 1 used in thefirst embodiment. Referring to FIGS. 2A and 2B, a basic segment 10 ofthe phase shifter 1 includes first and second regions 11 and 12 of arectangular shape formed on both sides of a straight boundary 10 a, anda small region 13 of a circular shape formed to extend into the firstand second regions 11 and 12. The small region 13 includes a first smallsector 13 a which is a semicircular region formed in the first region11, and a second small sector 13 b which is a semicircular region formedin the second region 12.

The first region 11 and the second region 12 are configured to transmitlight by a first phase retardation of 180 degrees therebetween. Thefirst and second small sectors 13 a and 13 b are configured to transmitlight by a second phase retardation of 60 degrees with respect to thefirst and second regions 11 and 12. Further, a phase retardation of 180degrees is given between the lights transmitted through the first andsecond small sectors 13 a and 13 b.

Concretely, when the phase shifter 1 is formed, for example, of quartzglass having a refractive index of 1.5 with respect to a light having awavelength of 248 nm, a step of 248 nm is provided between the first andsecond regions 11 and 12. The first small sector 13 a is formed as aconcave to provide a step of about 82.7 nm between the first region 11and first small sector 13 a. The second small sector 13 b is formed as aconcave to provide a step of about 82.7 nm between the second region 12and second small sector 13 b. A step of 248 nm is provided between thefirst small sector 13 a and second small sector 13 b. Moreover, thesmall region 13 also serves as the phase-shift section as describedlater. In addition, the phase shifter 1 includes a plurality of basicsegments 10 arrayed two-dimensionally.

In the first embodiment, the phase shifter 1 has a phase-shift patternformed as a combination of the above-described linear and circular phaseshifters in a surface facing the sample substrate 3. The functions oflinear and circular phase shifters will be described prior to thefunction of the phase shifter 1 provided in the first embodiment.

FIGS. 3A to 3D are diagrams for explaining the function of the linearphase shifter. If the linear phase shifter is applied to the firstembodiment, as shown in FIG. 3A, the phase shifter includes two regions31 a and 31 b having a phase retardation of 180 degrees therebetween,for example. A straight boundary 31 c between two regions 31 a and 31 bserves as the phase-shift section. This provides a light intensitydistribution on the sample substrate 3, as shown in FIG. 3B. The lightintensity distribution has an inverse peak pattern in which the lightintensity is substantially 0 on an axis 32 corresponding to thephase-shift section (straight boundary) and one-dimensionally increasestoward the outside in a direction perpendicular to the axis 32.

In this case, as shown in FIG. 3C, a temperature distribution is lowestalong the axis 32 corresponding to the phase-shift section, and atemperature gradient (shown by arrows in the figure) is generated in thedirection perpendicular to the axis 32 corresponding to the phase-shiftsection.

That is, as shown in FIG. 3D, crystal nuclei 33 are created on the axis32 corresponding to the phase-shift section, and crystallizationproceeds from the crystal nuclei 33 in the direction perpendicular tothe axis 32 corresponding to the phase-shift section.

In FIG. 3D, curves 34 indicate crystal grain boundaries. Crystal grainsare formed in regions defined by the crystal grain boundaries 34. Thecrystal nuclei 33 are created on the axis 32 corresponding to thephase-shift section, but a position on the axis 32 where the crystalnuclei are created is indefinite. In other words, when the linear phaseshifter is applied to the first embodiment, it is impossible to specifythe position where the crystal nucleus is created. Thus, it is alsoimpossible to two-dimensionally control a region where the crystal grainis formed. More specifically, it is impossible to control the regionoccupied by the crystal grain to include a region 35 reserved forforming a channel of a TFT.

FIGS. 4A to 4D are diagrams for explaining the function of the circularphase shifter. If the circular phase shifter is applied to the firstembodiment, as shown in FIG. 4A, the circular phase shifter includes arectangular region 41 a and a circular small region 41 b having a phaseretardation of 60 degrees (or 180 degrees) by which the phase leads withrespect to the rectangular region 41 a, for example. The circular smallregion 41 b serves as the phase-shift section. Therefore, on the samplesubstrate 3, as shown in FIG. 4B, the light intensity distribution ofthe inverse peak pattern is obtained in which the light intensity issubstantially 0 on a small part 42 corresponding to the phase-shiftsection and the light intensity increases toward the outside radiallyfrom the small part 42.

In this case, as shown in FIG. 4C, the temperature distribution islowest in the small part 42 corresponding to the phase-shift section,and the temperature gradient (shown by arrows in the figure) is radiallygenerated toward the outside from the small part 42 corresponding to thephase-shift section. That is, as shown in FIG. 4D, a plurality ofcrystal nuclei 43 (only one crystal nucleus is shown for clarificationof drawing in FIG. 4D) are created in or around the small part 42corresponding to the phase-shift section, and the crystallizationradially proceeds toward the outside from the plurality of crystalnuclei 43.

When the circular phase shifter is applied to the first embodiment inthis manner, the plurality of crystal nuclei 43 are created in or aroundthe small part 42 corresponding to the phase-shift section, and it istherefore possible to control the positions where the crystal nuclei 43are to be created. However, since the crystal grains grow from thecrystal nuclei 43 radially and simultaneously, positions where crystalgrain boundaries 44 are formed are indefinite, and it is impossible totwo-dimensionally control the regions where the crystal grains areformed. Concretely, it is impossible to control the region occupied bythe crystal grain to include a region 45 reserved for forming a channelof a TFT.

The first embodiment uses a defocus method in which the phase shifter isdisposed substantially in parallel with and in the proximity of thesample substrate. If the defocus method is also applied to the circularphase shifter, the light intensity in the small part 42 corresponding tothe phase-shift section can be smallest by providing a phase retardationof about 60 degrees between the rectangular region 41 a and circularsmall region 41 b. On the other hand, a second embodiment describedlater uses a projection NA method. If the projection NA method isapplied to the circular phase shifter, the light intensity in the smallpart 42 corresponding to the phase-shift section can be smallest byproviding a phase retardation of about 180 degrees between therectangular region 41 a and circular small region 41 b.

It is to be noted that for further detailed configurations or functionsof the linear and circular phase shifters, “Optimization ofphase-modulated excimer-laser annealing method for growing highly-packedlarge-grains in Si thin-films”, Applied Surface Science 154 to 155(2000) 105 to 111 can be referred to.

FIGS. 5A to 5C are diagrams for briefly explaining the function of thephase shifter 1 of the first embodiment. FIG. 6 is a diagram forexplaining the function of the phase shifter 1 in further detail. Asdescribed above, the phase shifter 1 of the first embodiment has aphase-shift pattern obtained by combining the linear phase-shift patternwith the circular phase-shift pattern. Therefore, on the samplesubstrate 3, as shown in FIG. 5A, the light intensity is substantially 0and smallest in a circular part 51 corresponding to the circular smallregion 13 which serves as the phase-shift section in the phase shifter1.

Moreover, a straight part 52 corresponding to the boundary 10 a of thephase shifter 1 has the next smallest light intensity to the circularpart 51. On the other hand, in a peripheral part 53 other than thecircular part 51 and straight part 52, as schematically shown by contourlines 54 indicating an equal light intensity, the light intensityincreases toward the outside in the direction perpendicular to thestraight part 52. With reference to FIG. 6, description will be made indetail about the feature that the light intensity in the circular part51 is lower than that in the straight part 52 and the light intensityincreases toward the outside in the direction perpendicular to thestraight part 52.

Referring to FIG. 6, the line A—A crosses the circular part 51 in adirection perpendicular to the straight part 52, and the line B—Bcrosses the straight part 52 in the direction perpendicular to thestraight part 52. When the illumination light incident upon the phaseshifter 1 is a parallel luminous flux (that is, the numerical apertureNA1 for the illumination light=0), a light intensity distribution alongthe line A—A is obtained in a manner that the light intensity issubstantially 0 in the circular part 51 and substantially constant inthe peripheral part 53 a, and a light intensity distribution along theline B—B is obtained in a manner that the light intensity issubstantially 0 in the straight part 52 and significantly increasestoward the peripheral part 53 to reach a constant value.

On the other hand, when the numerical aperture NA1 for the illuminationlight incident upon the phase shifter 1 is at a preset valuesubstantially larger than 0, the light intensity distributions along thelines A—A and B—B are influenced by a blur amount d·tan θ, where d is adistance between the sample substrate 3 and the phase shifter 1, and θis a maximum incidence angle of the illumination light to the phaseshifter 1. As a result, the light intensity distribution along the lineA—A has an inverse peak pattern in which the light intensity issubstantially 0 in the center of the circular part 51 and significantlyincreases toward the peripheral part 53 to substantially reach theconstant value.

Further, the light intensity distribution along line B—B has a U-shapedpattern that the light intensity indicates a substantially constantvalue remarkably greater than 0 in a wider part extended from thestraight part 52 by the blur amount d·tan θ and indicates, in peripheralpart 53 outer than the wider part, another substantially constant valuegreater than that in the wider part. Generally, when the numericalaperture NA1 for the illumination light is enlarged (that is, maximumincidence angle θ of the illumination light is enlarged), the bluramount d·tan θ influencing the light intensity distribution increases.Therefore, the light intensity in the straight part 52 increases.

However, when the blur amount d·tan θ is within a preset range, that is,when the numerical aperture NA1 for the illumination light is within thepreset range, the light intensity in the circular part 51 maintains avalue of substantially 0. In view of the above, the numerical apertureNA1 of the preset value is provided for the illumination light to beapplied to the phase shifter 1 in the first embodiment. Thus, the lightintensity distribution obtained on the sample substrate 3 has an inversepeak pattern that the light intensity is substantially 0 in the circularpart 51, higher in the straight part 52 than in the circular part 51,and significantly increases toward the outside from the circular part 51in the direction perpendicular to the straight part 52.

The width of the inverse peak pattern changes in proportion to ½ squareof a distance between the phase shifter 1 and sample substrate 3 (i.e.,defocus amount). In this case, the temperature is lowest in the circularpart 51, and the temperature gradient indicated by the arrow in FIG. 5Bis generated in the direction perpendicular to the straight part 52.Thus, as shown in FIG. 5C, a crystal nucleus 55 is created in or in thevicinity of the circular part 51 corresponding to the phase-shiftsection, and crystallization proceeds from the crystal nucleus 55 in thedirection perpendicular to the straight part 52.

As a result, the creation point of the crystal nucleus 55 is limited tothe circular part 51 or the vicinity. Moreover, the growth direction ofthe crystal grain from the crystal nucleus 55 is one-dimensionallylimited to a direction perpendicular to the straight part 52. Thus, theposition of the crystal grain boundary 56 is substantially controllable.That is, it is possible to two-dimensionally control a region where asingle-crystal grain 57 is formed, by specifying the positions of thecrystal nucleus 55 and the crystal grain boundary 56. More specifically,it is impossible to control the region occupied by the crystal grain 57to include a region 58 reserved for forming a channel of a TFT.

In the first embodiment, the light intensity distribution along the lineA—A transversely crossing the circular part 51 corresponding to thephase-shift section is actually obtained by simulation following aspecific numeric value examples. In the numeric value examples, thesmall region 13 has a regular octagonal shape inscribed with a circlehaving a radius of 1 μm, the distance d between the sample substrate 3and phase shifter 1 is 8 μm, and a wavelength λ of the illuminationlight is 248 nm. Moreover, the numerical aperture NA1 for theillumination light is set to NA1=1 and NA1=0.1 in the examples.

FIGS. 7A and 7B are diagrams showing the light intensity distributionobtained along the line A—A transversely crossing the circular region 51corresponding to the phase-shift section in the numeric value examplesin which the numerical aperture NA1 for the illumination light is set toNA1=0 and NA1=0.1. From the simulation results shown in FIGS. 7A and 7B,it is confirmed that a light intensity distribution substantiallyidentical to that along the line A—A schematically shown in FIG. 6 isobtainable in any of the cases where the numerical aperture NA1 for theillumination light is set to NA1=0 and NA1=0.1.

In this manner, in the first embodiment, sufficient lateral growth of acrystal grain from the crystal nucleus 55 is realized, and the crystalgrain can have a large diameter in the crystallized semiconductor film.Particularly, the mobility of the large crystal grain is high in thedirection of the lateral growth. Therefore, a transistor havingsatisfactory characteristics can be produced in the crystal grain if thesource-drain path thereof is set in the direction of the lateral growth.

It is to be noted that in the first embodiment the following conditionequation (1) is preferably satisfied:a≧d·tan θ  (1),where θ is the maximum incidence angle of the illumination lightincident upon the phase shifter 1, and d is the distance (gap) betweenthe sample substrate 3 (a non-single-crystal semiconductor film such aspolycrystalline or amorphous semiconductor film) and the phase shifter1. Moreover, a is a dimension of the first small sector 13 a or thesecond small sector 13 b in the direction perpendicular to the boundary10 a, and is equivalent to the radius of the small region 13 in thefirst embodiment.

As described above, the right side of the condition equation (1)represents the blur amount generated when the illumination lightincident upon the phase shifter 1 is not the parallel luminous flux.Therefore, when the condition equation (1) is satisfied, it is possibleto secure that the light intensity on the sample substrate 3 issubstantially 0 in the part 51 corresponding to the circular smallregion 13 serving as the phase-shift section. In other words, when thecondition equation (1) is not satisfied, the lowest value of the lightintensity is substantially greater than 0 in the part 51 on the samplesubstrate 3, and the desired light intensity distribution of the inversepeak pattern cannot be obtained.

FIG. 8 is a diagram schematically showing the configuration of thecrystallization apparatus according to a second embodiment of thepresent invention. FIG. 9 is a plan view for schematically showing theconfiguration of the basic segment 10 of the phase shifter 1 in thesecond embodiment. The second embodiment is similar to the firstembodiment in the configuration, but is basically different from thefirst embodiment in that the sample substrate 3 and the phase shifter 1are located at positions optically conjugated with respect to an opticalimaging system 5. The second embodiment will be described so as toclarify the difference. In FIG. 8, the internal configuration of theillumination system 2 is omitted for simplification.

In the second embodiment, the optical imaging system 5 is disposedbetween the phase shifter 1 and sample substrate 3 to locate the phaseshifter 1 and sample substrate 3 at the optically conjugated positions.In other words, the sample substrate 3 is set in a plane opticallyconjugated with the phase shifter 1 (image plane of the optical imagingsystem 5). An aperture diaphragm unit 5 a is disposed in an iris planeof the optical imaging system 5. The aperture diaphragm unit 5 aincludes a plurality of aperture diaphragms different from one anotherin the size of the aperture (light transmission portion), and theseaperture diaphragms can be changed with respect to an optical path.

Moreover, the aperture diaphragm unit 5 a may also be formed of an irisdiaphragm that can continuously change the size of the aperture. In anycase, the size of the aperture of the aperture diaphragm unit 5 a(numerical aperture NA on the imaging side of the optical imaging system5) is set to obtain a required light intensity distribution of theinverse peak pattern on the semiconductor film of the sample substrate3. In addition, the optical imaging system 5 may be a refractive opticalsystem, reflective optical system, or a refractive and reflectiveoptical system.

Referring to FIG. 9, the phase shifter 1 of the second embodimentincludes basically the same configuration as that of the phase shifter 1of the first embodiment. That is, the shifter includes the first region11, second region 12, and small region 13, and the phase retardation of180 degrees is given as the first phase retardation between thetransmitted lights of the first region 11 and second region 12. However,in the second embodiment, different from the first embodiment, the phaseretardation of 180 degrees is given as the second phase retardationbetween the transmitted lights of the first region 11 and first smallsector 13 a and between the transmitted lights of the second region 12and second small sector 13 b.

Concretely, for example, when the phase shifter 1 is formed of quartzglass having a refractive index of 1.5 with respect to the light havinga wavelength of 248 nm, a step of 248 nm is disposed between the firstand second regions 11 and 12. The step of 248 nm is also disposedbetween the first region 11 and first small sector 13 a and between thesecond region 12 and second small sector 13 b. The step of 248 nm isalso disposed between the first small sector 13 a and second smallsector 13 b. Moreover, the second embodiment is similar to the firstembodiment in that the small region 13 serves as the phase-shift sectionand that the phase shifter 1 includes a plurality of basic segments 10arrayed two-dimensionally.

In the second embodiment, the width of the inverse peak pattern obtainedon the semiconductor film of the sample substrate 3 by means of thephase shifter 1 is of the same degree as that of a resolution R of theoptical imaging system 5. Assuming that the wavelength of the light foruse is λ and the numerical aperture of the optical imaging system 5 onthe imaging side is NA, the resolution R of the optical imaging system 5is defined by R=kλ/NA, where a constant k indicates a valuesubstantially close to 1 depending on specifications of the illuminationsystem 2 for illuminating the phase shifter 1, degree of coherence ofthe luminous flux supplied from the light source 2 a, and definition ofthe resolution. In this manner, in the second embodiment, when theimage-side numerical aperture NA of the optical imaging system 5 isreduced, and the resolution of the optical imaging system 5 is lowered,the width of the inverse peak pattern increases.

Also in the second embodiment, in the same manner as in the firstembodiment, the creation point of the crystal nucleus is limited to apart corresponding to the phase-shift section of the phase shifter 1,and the growth direction of the crystal grain from the crystal nucleusis one-dimensionally limited. Thus, the position of the crystal grainboundary is substantially controllable. That is, it is possible totwo-dimensionally control a region where a single-crystal grain isformed, by specifying the positions of the crystal nucleus and thecrystal grain boundary.

It is to be noted that in the first embodiment the phase shifter 1 iscontaminated by abrasion in the sample substrate 3, and furthersatisfactory crystallization is sometimes inhibited. On the other hand,in the second embodiment, the optical imaging system 5 is locatedbetween the phase shifter 1 and sample substrate 3, and a relativelylarge gap is secured between the sample substrate 3 and optical imagingsystem 5. Therefore, the satisfactory crystallization can be realizedwithout being influenced by the abrasion in the sample substrate 3.

Moreover, in the first embodiment, since the phase shifter 1 and samplesubstrate 3 should be spaced by a very small distance (e.g., severalmicrometers to several hundreds of micrometers), it is difficult toguide a detection light for detecting the alignment position into anarrow optical path between the phase shifter 1 and sample substrate 3,and it is also difficult to adjust the distance between the phaseshifter 1 and sample substrate 3. On the other hand, since a relativelylarge distance is secured between the sample substrate 3 and opticalimaging system 5 in the second embodiment, it is easy to guide thedetection light for detecting the alignment position into the opticalpath and to adjust the alignment between the sample substrate 3 andoptical imaging system 5.

It is to be noted that in the second embodiment the following conditionequation (2) is preferably satisfied.a≦λ/NA  (2),where NA denotes the numerical aperture of the optical imaging system 5on the imaging side, λ is the wavelength of the light, and a denotes thedimension of the first small sector 13 a or the second small sector 13 bin the direction perpendicular to the boundary 10 a.

As described above, the right side of the condition equation (2)represents the resolution of the optical imaging system 5. Therefore,when the condition equation (2) is satisfied, the dimension of the firstsmall sector 13 a or the second small sector 13 b is not more than theresolution. On the sample substrate 3, an area whose light intensity issubstantially 0 does not have a hollow annular shape, but a solidcircular shape within the part 51 corresponding to the circular smallregion 13 serving as the phase-shift section. In other words, when thecondition equation (2) is not satisfied, the area whose light intensityis substantially 0 has the annular shape in the part 51 of the samplesubstrate 3, and the light intensity distribution having a desired peakpattern cannot be obtained.

Concretely, when the numerical aperture NA of the optical imaging system5 on the imaging side is excessively large, two inverse peak patternsare provided in parallel as the light intensity distribution. Thus, thelight intensity distribution having a desired peak pattern cannot beobtained. On the other hand, when the image-side numerical aperture NAof the optical imaging system 5 is excessively small, the lightintensity distribution having a desired inverse peak pattern cannot beobtained since the lowest light intensity increases from a value ofsubstantially 0.

In the above-described embodiments, the phase retardation of 180 degreesis given as the first phase retardation between the transmitted lightsof the first region 11 and second region 12 in the phase shifter 1. Inthis case, not only the lowest light intensity can be obtained in thestraight part 52 corresponding to the boundary 10 a of the phase shifter1, but also the light intensity distribution can be symmetrical withrespect to the straight part 52. However, for example, when it isintended that the crystallization proceeds toward one side of thestraight part 52, the phase retardation substantially different from 180degrees may also be given between the transmitted lights of the firstregion 11 and second region 12.

Moreover, in each of the embodiment described above, the small region 13is formed in the phase shifter 1 to have a circular shape extending intoboth the first region 11 and second region 12 and symmetrical withrespect to the boundary 10 a. However, the shape of the small region 13is arbitrary. This is apparent from the simulation in which a regularoctagonal shape is applied to the small region 13. For example, when itis intended that the crystallization proceeds toward one side of thestraight part 52, a shape projecting toward a corresponding side of theboundary 10 a. That is, in general, the small region serving as thephase-shift section may be formed to extend from the boundary 10 a intoat least one of the first and second regions 11 and 12.

Furthermore, as described above, the second phase retardation givenbetween the first region 11 and first small sector 13 a and between thesecond region 12 and second small sector 13 b is preferably about 60degrees in the defocus method of the first embodiment, and about 180degrees in the projection NA method in the second embodiment. When thesecond phase retardation is set in this manner, the light intensity inthe part 51 on the sample substrate 3 corresponding to the small region13 serving as the phase-shift section can be controlled substantially to0.

FIGS. 10A and 10B are diagrams showing the alignment between a crystalgrain and a channel formed in each embodiment in comparison with that ofa related art. Referring to FIG. 10B, in the related art using thelinear phase shifter, the crystal grains collide with one another whengrowing from the respective crystal nuclei created at random. Therefore,only very thin and long crystal grains are formed in the directionperpendicular to the axis 32 corresponding to the phase-shift section(boundary) of the linear phase shifter. Therefore, in the related art, aplurality of crystal grains are used to form a channel 61 of a thin filmtransistor.

On the other hand, in each embodiment, since the crystal nuclei areseparately created in or in the vicinity of the circular parts 51corresponding to the circular small regions 13 serving as thephase-shift section in the phase shifter 1, the crystal grains do notcollide with one another when growing from the crystal nuclei.Therefore, for the crystal grain 57 obtained using the crystallizationapparatus and method of each embodiment, as shown in FIG. 10A, a size Wof the crystal grain 57 in a direction parallel to the straight part 52corresponding to the boundary 10 a of the phase shifter 1 is relativelylarge as compared with a size L of the crystal grain 57 in the directionperpendicular to the straight part 52.

As a result, the channel 61 for the thin film transistor can be formedin the single crystal (crystal grain) 57 formed using thecrystallization apparatus and method of each embodiment. In this case,in the phase shifter 1 for use in the crystallization apparatus andmethod of each embodiment, the phase-shift pattern including the firstregion 11, second region 12, and small region 13 needs to be formed inthe area reserved for the channel 61 of the thin film transistor.

Moreover, a source 62 and drain 63 are formed on the sides of thechannel 61 in the direction perpendicular to the straight part 52corresponding to the boundary 10 a of the phase shifter 1. In addition,the size W of the crystal grain 57 is preferably ⅓ or more of the sizeL, and the size W of the crystal grain 57 is preferably 1 μm or more. Bythis configuration, it is possible to securely form the channel 61 inthe single crystal 57.

FIGS. 11A and 11B are diagrams showing a growth angle estimated from thestart point of crystal growth of the crystal grain formed in eachembodiment in comparison with that of the related art. Referring to FIG.11B, in the related art using the linear phase shifter, as shown bycontour lines 36 having an equal light intensity, the gradient of thelight intensity distribution (also the gradient of the temperaturedistribution) is straight. Therefore, a crystal grain 35 grows only inone direction, and an angle φ2 of the crystal grain 35 estimated fromthe start point of the crystal growth is very small.

On the other hand, in each embodiment, as shown by the contour lines 54having the equal light intensity, the gradient of the light intensitydistribution (the gradient of the temperature distribution) has a curvedshape around the circular part 51. Therefore, the crystal grain 57two-dimensionally grows, and an angle φ1 of the crystal grain 57estimated from the start point of the crystal growth is very large ascompared with the related art. As a result, the channel 61 (not shown inFIGS. 11A and 11B) is easily formed in the single crystal (crystalgrain) 57. Additionally, a distance between the start point of thecrystal growth and the channel 61 is minimized and miniaturization canbe achieved. For this purpose, the angle φ1 of the crystal grain 57estimated from the start point of the crystal growth is preferablywholly 60 degrees or more.

In each above-described embodiment, the light intensity distribution canbe calculated even in a stage of design, but it is preferable to observeand confirm the light intensity distribution on the sample surface(exposure surface). For this, an image of the sample surface may beenlarged by the optical system and inputted via image capture devicessuch as CCD. When the light for use is an ultraviolet ray, the opticalsystem is restricted. Therefore, a fluorescent plate may be disposed inthe sample surface to change the light to a visible light.

FIGS. 12A to 12E are sectional views showing steps of producing anelectronic device using the crystallization apparatus of eachembodiment. As shown in FIG. 12A, on an insulating substrate 80 (e.g.,alkali glass, quartz glass, plastic, polyimide, and the like), anunderlying film 81 (e.g., a laminate film of SiN having a film thicknessof 50 nm and SiO₂ having a film thickness of 100 nm) and an amorphoussemiconductor film 82 (e.g., Si, Ge, SiGe having a film thickness ofabout 50 nm to 200 nm) are formed using a chemical vapor growth methodor sputter method, so that the sample substrate 3 is prepared.Subsequently, the crystallization apparatus of each embodiment is usedto irradiate a part or all of the surface of the amorphous semiconductorfilm 82 with laser light 83 (e.g., KrF excimer laser light, XeCl excimerlaser light, and the like).

In this manner, as shown in FIG. 12B, a polycrystalline orsingle-crystal semiconductor film 84 including the crystal grain havinga large diameter is produced. Next, as shown in FIG. 12C, aphotolithography technique is used to process the polycrystalline orsingle-crystal semiconductor film 84 into an island-shaped semiconductorfilm 85, and an SiO₂ film having a film thickness of 20 nm to 100 nm isformed as a gate insulating film 86 using the chemical vapor growthmethod or sputter method. Furthermore, as shown in FIG. 12D, a gateelectrode 87 (e.g., silicide, MoW, and the like) is formed. The gateelectrode 87 is used as a mask to implant impurity ions 88 (phosphor foran N channel transistor, boron for a P channel transistor). Thereafter,an anneal process (e.g., at 450° C. for one hour) is performed in anitrogen atmosphere to activate impurities.

Next, as shown in FIG. 12E, an interlayer insulating film 89 is formed,contact holes are made, and a source electrode 93 and drain electrode 94connected to a source 91 and drain 92 are formed. The source isconnected to the drain via a channel 90. At this time, the channel 90 islocated within the crystal grain of the large diameter formed in thepolycrystalline or single-crystal semiconductor film 84 through thesteps shown in FIGS. 12A and 12B. With the above-described steps, apolycrystalline or single-crystal semiconductor transistor positioned asshown in FIG. 13 can be obtained. This polycrystalline or single-crystalsemiconductor transistor can be applied to driving circuits for a liquidcrystal display or electro luminescence (EL) display, integratedcircuits such as a memory (SRAM or DRAM) and CPU, and the like.

An example in which the transistor obtained as described above isactually applied to an active matrix liquid crystal display will bedescribed hereinafter.

FIG. 14 is a diagram schematically showing the circuit configuration ofthe liquid crystal display. FIG. 15 is a diagram schematically showing asectional structure of the liquid crystal display.

The liquid crystal display includes a liquid crystal display panel 100and a liquid crystal controller 102 for controlling the liquid crystaldisplay panel 100. The liquid crystal display panel 100 has a structurein which, for example, a liquid crystal layer LQ is held between anarray substrate AR and a counter substrate CT. The liquid crystalcontroller 102 is disposed on a driving circuit substrate disposedseparately from the liquid crystal display panel 100.

The array substrate AR includes a plurality of pixel electrodes PEarrayed in a matrix form within a display region DS on a glasssubstrate, a plurality of scanning lines Y (Y1 to Ym) formed along rowsof the pixel electrodes PE, a plurality of signal lines X (X1 to Xn)formed along columns of the pixel electrodes PE, pixel switchingelements 111 which are disposed near intersections of the signal linesX1 to Xn and the scanning lines Y1 to Ym and each of which captures avideo signal Vpix from a corresponding signal line X in response to ascanning signal from a corresponding scanning line Y to supply thesignal to a corresponding pixel electrode PE, a scanning line drivingcircuit 103 for driving the scanning lines Y1 to Ym, and a signal linedriving circuit 104 for driving the signal lines X1 to Xn. Each pixelswitching element 111 is formed, for example, of an N-channel thin filmtransistor formed as described above. The scanning line driving circuit103 and signal line driving circuit 104 are integrated on the arraysubstrate AR by thin film transistors formed along with the thin filmtransistors of the pixel switching elements 111 in the same manner asthat of each embodiment described above. The counter substrate CTincludes a single counter electrode CE disposed to face the pixelelectrodes PE and set to a common potential Vcom, a color filter (notshown), and the like.

The liquid crystal controller 102 receives a video signal andsynchronous signal supplied externally, for example, to generate a videosignal Vpix for pixels, vertical scanning control signal YCT, andhorizontal scanning control signal XCT. The vertical scanning controlsignal YCT includes, for example, a vertical start pulse, vertical clocksignal, output enable signal ENAB, and the like, and is supplied to thescanning line driving circuit 103. The horizontal scanning controlsignal XCT includes a horizontal start pulse, horizontal clock signal,polarity reverse signal, and the like, and is supplied to the signalline driving circuit 104 together with the pixel video signal Vpix.

The scanning line driving circuit 103 includes a shift register, and iscontrolled by the vertical scanning control signal YCT so as tosequentially supply a scanning signal for energizing the pixel switchingdevice 111 to the scanning lines Y1 to Ym every vertical scanning(frame) period. The shift register shifts the vertical start pulsesupplied every vertical scanning period in synchronization with thevertical clock signal to select one of the scanning lines Y1 to Ym, andrefers to the output enable signal ENAB to output the scanning signal tothe selected scanning line. The output enable signal ENAB is maintainedat a high level so as to permit the output of the scanning signal in aneffective scanning period in the vertical scanning (frame) period. Thesignal is maintained at a low level so as to prohibit the output of thescanning signal in a vertical blanking period obtained by excluding theeffective scanning period from the vertical scanning period.

The signal line driving circuit 104 includes a shift register and sampleoutput circuit, and is controlled by the horizontal scanning controlsignal XCT to serial-parallel convert or sample the video signal Vpixinput in each horizontal scanning period (1H) during which one scanningline Y is driven by the scanning signal, and supply analog pixel displaysignals obtained by sampling to the signal lines X1 to Xn.

In this liquid crystal display, the thin film transistors of thescanning line driving circuit 103 and signal line driving circuit 104can be formed in a process common to the thin film transistors of thepixel switching elements 111.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventionconcept as defined by the appended claims and their equivalents.

1. A crystallization apparatus comprising: an illumination system whichapplies illumination light for crystallization to a non-single-crystalsemiconductor film; a phase shifter which includes first and secondregions disposed to form a straight boundary and transmitting theillumination light from said illumination system by a first phaseretardation therebetween, and phase-modulates the illumination light toprovide a light intensity distribution having an inverse peak patternthat light intensity falls in a zone of said non-single-crystalsemiconductor film containing an axis corresponding to said boundary;said phase shifter further including a small region which extends intoat least one of said first and second regions from said boundary andtransmits the illumination light from the illumination system by asecond phase retardation with respect to said at least one of said firstand second regions.
 2. The crystallization apparatus according to claim1, wherein said small region has a first small sector which is formed insaid first region and transmits the illumination light by the secondphase retardation with respect to said first region, and a second smallsector which is formed in said second region and transmits theillumination light by the second phase retardation with respect to saidsecond region.
 3. The crystallization apparatus according to claim 1,wherein the first phase retardation is about 180 degrees.
 4. Thecrystallization apparatus according to claim 1, wherein said smallregion has a shape symmetrical with respect to said boundary.
 5. Thecrystallization apparatus according to claim 1, wherein said phaseshifter is disposed in parallel with and in the proximity of saidnon-single-crystal semiconductor film.
 6. The crystallization apparatusaccording to claim 5, wherein the second phase retardation is about 60degrees.
 7. The crystallization apparatus according to claim 6, whereinsaid small region has a size a in a lateral direction perpendicular tosaid boundary within said at least one of said first and second regions,and said size a satisfies a condition a≧d·tan θ which depends on amaximum incidence angle θ of the illumination light incident upon saidphase shifter and a distance d between said non-single-crystalsemiconductor film and said phase shifter.
 8. The crystallizationapparatus according to claim 1, further comprising an optical imagingsystem disposed between said non-single-crystal semiconductor film andsaid phase shifter to locate said non-single-crystal semiconductor filmand phase shifter at positions conjugated with each other, and thenumerical aperture of said optical imaging system on an imaging sidebeing set a preset value required for the light intensity distributionhaving said inverse peak pattern.
 9. The crystallization apparatusaccording to claim 8, wherein the second phase retardation is about 180degrees.
 10. The crystallization apparatus according to claim 8, whereinsaid lateral size a satisfies a condition a≦λ/NA depending on theimaging-side numerical aperture NA of said optical imaging system and awavelength λ of the illumination light.
 11. The crystallizationapparatus according to claim 5, wherein said small region has a size ain a lateral direction perpendicular to said boundary within said atleast one of said first and second regions, and said size a satisfies acondition a≧d·tan θ which depends on a maximum incidence angle θ of theillumination light incident upon said phase shifter and a distance dbetween said non-single-crystal semiconductor film and said phaseshifter.